1. Field of the Invention
The purpose of this invention is to provide a digital memory area correlation tracking device with continuous television display of the tracked area. In particular it is intended to provide a device for supplying information on the displacement of a scene with respect to its original position as viewed from a sensor such as a television camera, radar, or other sensing device and to provide means for reducing this displacement to zero.
2. Description of the Prior Art
A multiplicity of tracking devices working on electro-optical principles are known. They can be divided into two types: systems tracking an isolated point of the scene which exhibits characteristics different from its surroundings; and systems which use information from sources other than the point tracked. The first type of systems requires that the point to be tracked is sufficiently different from the background and that its characteristics are not subject to rapid, random change; this type of system will consequently fail if the noise level in the system exceeds the difference between the target and its surroundings. The second type of system has various embodiments. One of these embodiments requires a photographic positive or negative to be correlated with the actual scene. The need for the photographic reference is clearly a disadvantage in systems employed against targets which cannot be pre-determined. Another embodiment requires an annular ring of information from around the target to be stored in a memory and correlated against sequential information obtained from the sensing device. In such a system it is extremely difficult to obtain an accurately boresighted television image of the target scene and to determine the actual aim point of the system. Furthermore, a change in aim point in such a system requires that the tracking operation be interrupted and that a new reference signal be stored. Still another embodiment requires a television signal to be stored in analog form in an electron beam storage tube. The stored signal is read out of the storage tube with the same scan signals as it was read in, but an additional scan is added. The readout signal is then compared in analog form with the new signal from the camera and the resultant signal is then delayed and gated to produce an error signal for correcting the line of sight. The necessity of a storage tube in this system results in many noise disadvantages.